1. Field of the Invention
The present invention relates to a picture image data processor used in a facsimile system or the like.
2. Description of the Related Art
In order to efficiently transmit more picture data with a constant transmission rate, a prior art picture image data processor used in a facimile system converts a picture image data read out from an original document and corresponding to two lines, to a picture image data corresponding to one line for its transmission.
In this case, the transmission of data only by omitting the one-line data causes thin or fine lines of the original document picture to be lost so that, when the data is received and reproduced at the side of a receiver the received data is not exactly the same as the original data, that is, the data is not correctly transmitted. In order to reproduce the original data correctly without any omission of the fine lines at the side of the receiver, it has been common practice to process the original data in accordance with the following logical operational expression to convert a picture image data of the original document corresponding to two lines to a picture image data corresponding to one line and then transmit it to the receiver side. EQU C'=B+C (1)
where C' denotes a transmitting picture image data subjected to a logical operation and corresponding to one line, C denotes a picture image data on the current scanning line and B denotes a picture image data on the previous scanning line. When the read picture image data corresponding to two lines is converted to a picture image data corresponding to one line and then transmitted to the receiver side on the basis of the logical expression (1), the amount of data to be processed can be doubled with a constant transmission rate, so that the picture processing efficiency can be increased and the original picture can be correctly reproduced at the receiving side without loss of any fine lines.
The use of such data transmission system based on the coversion from two-line data to one-line data according to the expression (1) usually enables the picture data to be extracted and reproduced at the receiver side without loss of any fine lines of the black picture elements. However, if the previous line corresponds to a black line and the subsequent line corresponds to a white fine line, then the white fine line cannot be reproduced at the receiver side. That is, supposing that a black line is expressed by "1" and a white line is by "0", if the previous lines are all black ones and the corresponding subsequent lines are all white one, then the white fine lines cannot be reproduced at the receiver side, because the logical expression (1) is written as EQU 1=1+O
which means that the converted picture image data all refer to black.